The present invention relates generally to interconnection technology, and more particularly to micro-soldering technology used for component packaging of integrated circuit devices.
Soldering is a widely used interconnection technology for component packaging and is used in many applications including, without limitation, Flip-Chip, Chip Scale Packaging (CSP), Multi-Chip Module (MCM), Ball Grid Array (BGA), Chip-on Glass (COG), Chip-on Board (COB), and wafer level packaging. Basic soldering process includes steps of solder deposition and solder reflow. First, solder is deposited (usually via evaporation or electroplating) on active devices such as integrated circuit chips (IC""s) or, more typically, on a module to which the IC""s are to be attached. Then, the module and the IC""s are soldered together to form, for example, a multi-chip module, or MCM. The soldering is performed by placing the IC""s on the module (so as to have the deposited solder posited between the module and the IC""s) and reflowing the solder by heat. To apply the necessary heat, the entire MCM is placed in an oven. During the reflow process, the solder melts, reflows, and solidifies when cooled resulting in a bond between the module and the IC""s. With the increasing demand for miniaturized systems and ultra-fine packaging, soldering method has became one of the popular technology for die attachment to form the MCM""s, BGA""s, and the like.
In conventional electronics component packaging and assembly technology, during the reflow step of the soldering process, the entire component are heated together including the module and all the devices attached to the module. Typically, a number of active devices are soldered on to a module, and the active devices may include different types of circuits, made with different materials, or both. Several problems arise due to the heating processes. First, the active devices and the module likely have different thermal stress tolerances, different thermal expansion coefficients, and different heat retention and radiation characteristics. These differences may lead to mechanical failures such as bad contacts. Second, one or more devices may fail because of the thermal stress. Third, because of these differences, it is difficult to control the reflow temperature and timing requirements. Fourth, once the component packaging is soldered, it is difficult to rework at the die level. That is, if a bad device is found on a soldered, packaged MCM, the bad device is not likely to be replaced, and the entire component may be scrapped.
To alleviate these problems localized heating methods have been used with some success. For example, electrical induction heating technology uses electromagnetic fields to induce current around a solder area to generate heat to reflow the solder. A drawback of this technology is that the induced current may damage the devices. Another example is laser-welding technology. In laser welding process, laser beam is focused on solder areas to generate heat to melt the solder. Here, a portion of the photon energy from the laser is absorbed by the devices and is converted to thermal energy. The thermal energy may damage the device. Further, laser-welding systems are very complex thereby limiting its widespread use.
Both the electrical induction heating method and the laser welding method have limitation for Flip-Chip application like BGA and CSP because the induction current or laser beam energy has to penetrate the device from the top, or the backside, in order to generate heat to the solder. During that heat generation process, the inductive current (for the induction heating technique) or the photon energy (for the laser welding technology) is absorbed by the devices causing local thermal stress and global thermal expansion across the MCM.
Accordingly, there remains a need for technology to package devices onto a module without damage to the devices or to the module.
These needs are met by the present invention. According to one aspect of the present invention, an apparatus such as a module includes a heating circuit having a resistor layer and a conductor layer patterned to define a current path, the current path including a portion of the resistor layer.
To attach the active devices to the module, solder is deposited onto the module. Then, the active devices are placed on the module. Next, current is applied to the heating circuit whereby heat is generated, reflowing the solder to attach the active devices to the module.
According to another aspect of the present invention, an apparatus having an electrically localized heating circuit is manufactured by fabricating a resistor layer on a substrate and fabricating a patterned conductor layer, the pattern defining a current path, the current path including a portion of the resistor layer.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.